Think back to playing Goldeneye multiplayer. Or Halo. The absolute worst thing you could do was to "cheat" by looking at your opponent's screen. Well, there's now a video game that's all about that cheating.
It's called, appropriately, Screencheat, which Nathan covered earlier in the year but which I played a bit of over the weekend. It's a fairly simple multiplayer shooter with a very different twist: everyone is invisible. So you have to look at your opponent's screen, since that's the only way you can play the game.
It certainly takes some getting used to, as the way we've been trained to play a shooter is so instinctual that forcing yourself to look away from your portion of the screen is hard work. But once it comes together, it's a blast. Games of Screencheat are utterly chaotic in the best possible way, players flailing around a map shooting into empty rooms and killing people all the time, sometimes on purpose, sometimes completely by accident.
If you're thinking the game sounds impossible, there are a few things helping you out. The maps are divided into clear identifiable sections, either by colour or design, so that you can quickly and easily get an idea of where your opponents are. Your characters aren't entirely invisible, either; every time you discharge or swing a weapon, the muzzle flash/swipe action shows up, giving everyone a precise (if momentary) glimpse at your location.
Screencheat is $10 on Steam. It's out on sometime in October.